The present invention relates to an automotive road wheel and an attaching structure of the same. More specifically, the present invention relates to an automotive road wheel having its sound vibration performance improved without any substantial reductions in driving stability, and to an attaching structure of the same.
Generally, the automotive road wheel was mounted on an axle portion connected to a car body through a suspension or the like by fastening its disk portion with bolts and nuts, accordingly achieving both driving stability and sound vibration performance. In recent years, however, with the appearance of higher-class type passenger cars, there have been stronger requests for further improvements, especially on ride comfort and sound vibration performance with respect to road noise or the like.
As a countermeasure for such requests, Japanese patent application Kokai publication No. 6-344703 proposes a road wheel, which is designed to damp vibration by spot-welding a plurality of places in a circumferential direction between the disk portion and a rim portion separated from each other, and by providing a viscoelastic substance such as asphalt, rubber or the like in a nonwelded portion. However, according to this countermeasure, since the disk portion and the rim portion had to be prepared as components independent of each other, it was impossible to use an existing road wheel, necessitating the preparation of a new metal mold as a dedicated wheel. Consequently, the conventional road wheel had drawbacks including an increase in manufacturing costs, designing constraints, etc.
An object of the present invention is to provide an automotive road wheel, which is capable of improving sound vibration performance without any substantial reductions in driving stability only by reconstructing a part of a structure of an existing road wheel.
Another object of the present invention is to provide an attaching structure of an automotive road wheel, which is capable of improving sound vibration performance without any substantial reductions in driving stability while maintaining a road wheel of a conventional structure intact.
In order to achieve the first object described above, in accordance with the present invention, an automotive road wheel is provided, comprising: a disk portion fixed to an axle portion of a vehicle by a fastener; and a vibration isolation mechanism provided in a place of fixing the disk portion by the fastener.
Since the vibration isolation mechanism is provided in the place where the disk portion is fastened to the axle portion of the vehicle, vibration transmitted from a tire through the disk portion to the axle portion is damped by the vibration isolation mechanism, thereby improving the sound vibration performance. Moreover, since an amount of displacement in the fastening place in an axial direction is small, no substantial reductions occur in the driving stability.
In addition, since the vibration isolation mechanism can be mounted only by partially reconstructing an existing road wheel structure, a metal mold for the conventional road wheel can be directly used, enabling lowxe2x80x94cost manufacturing.
In order to achieve the second object described above, in accordance with the present invention, an attaching structure of an automotive road wheel is provided, comprising: an axle hub attached to an axle configuration; a road wheel attached to the axle hub; and a vibration isolation mechanism provided between the axle configuration and the axle hub.
Since the vibration isolation mechanism is interposed between the axle configuration and the axle hub, the vibration transmitted from the tire through the disk portion of the road wheel to the axle portion is damped by the vibration isolation mechanism, thereby improving the sound vibration performance. Moreover, since the amount of the variable displacement in the axial direction is small, no substantial reductions occur in the driving stability. In addition, the vibration isolation mechanism can be mounted without any alterations to the existing road wheel at all, enabling the low-cost manufacturing.
According to the present invention, in any of the cases of the road wheel and its attaching structure, the vibration isolation mechanism is constructed regarding the damping material as a main portion. For the damping material, no particular limitation is placed as long as the material has a characteristic of damping the vibration transmitted from the road wheel to the axle portion. For example, enumerated can be rubber, thermoplastic resin, a thermoplastic resin elastomer composition prepared by blending the thermoplastic resin with rubber, and the like. Also, when necessary, a damping steel plate can be used as the damping material.
No particular limitation is placed on the rubber used for the damping material. Any of synthetic rubber and natural rubber can be used. Moreover, no particular limitation is placed on the thermoplastic resin, as long as it has a characteristic of damping vibration.
The thermoplastic resin elastomer composition has a viscoelastic characteristic, which is prepared by blending the thermoplastic resin with rubber. Especially, one is preferable, which is prepared in such a manner that the thermoplastic resin having a peak of tan xcex4 in a range of 0xc2x0 C. to 150xc2x0 C. is set to be a continuous phase, and a rubber component at least partially cross-linked and having a peak of tan xcex4 in a range of xe2x88x92100xc2x0 C. to 0xc2x0C. is dispersed in the continuous phase. In this case, a temperature indicating the peak of tan xcex4 is one, at which a temperature dependence curve of tan xcex4 is obtained under the condition of 20 Hz based on JIS K7198, and the curve indicates a peak.
For the rubber used for the thermoplastic resin elastomer composition, enumerated can be butyl-containing rubber, olefin-containing rubber, natural rubber and the like. In addition, for the thermoplastic resin, enumerated can be polyamide-containing resin, polypropylene-containing resin, polyester-containing resin and the like.
The structure of the vibration isolation mechanism used for the present invention preferably includes the damping material joined unitarily between the outer and inner cylinders. Also, it is preferable to join the damping material unitarily with the outer and inner cylinders by baking or adhesive. For the damping material, the foregoing material can be used, and for the outer and inner cylinders, metal such as copper, aluminum or the like, and fiber-reinforced resin can be used.
In such a unitary structure composed of the outer cylinder, the damping material and the inner cylinder, in the case of the road wheel of the present invention, the road wheel can be mounted by pressing the outer cylinder into the disk portion of the road wheel, and fixing the inner cylinder to the axle portion of the vehicle by the fastener such as bots and nuts. In the case of the vibration isolation mechanism described above, an amount xcex4b of variable displacement upon application of a load in a direction orthogonal to the axial direction of the fastener (up-and-down direction of the vehicle) is preferably set to be larger than an amount xcex4a of variable displacement upon application of the same load in the axial direction (left-and-right direction of the vehicle). Because of the large amount xcex4b of variable displacement in the direction orthogonal to the axial direction of the fastener, ride comfort and road noise are reduced. Because of the small amount xcex4a of variable displacement in the axial direction of the fastener, good driving stability is maintained without being lowered.
Means for obtaining the foregoing characteristic can be achieved by setting a thickness a of the damping material held in the axial direction of the fastener to be smaller than a thickness b held in a direction orthogonal to the axial direction, for example in the damping material provided between the outer and inner cylinders. In addition, the damping material provided between the outer and inner cylinders can be obtained by setting a difference in an elastic modulus between a damping material A held in the axial direction of the fastener and a damping material B held in the direction orthogonal to the axial direction, and by setting the elastic modulus of the damping material A to be larger than that of the damping material B.
In the case of the road wheel attaching structure of the present invention, the axle portion is a structure composed of the axle configuration and the axle hub, and the road wheel is fixed to the axle hub. When the axle configuration is a non-drive shaft, the axle hub is rotatably supported on the axle configuration by providing a bearing inside. When the axle configuration is a drive shaft, the axle hub is directly fixed to the drive shaft.
As in the case of the vibration isolation mechanism used for the road wheel, the structure of the vibration isolation mechanism used for the present invention preferably includes the damping material joined unitarily between the outer and inner cylinders. It is preferable to join the damping material unitarily with the outer and inner cylinders by baking or adhesive. The foregoing material is used for the damping material, and for the outer and inner cylinders, metal such a copper, aluminum or the like, fiber-reinforced resin and the like can be used.
In the automotive road wheel attaching structure of the present invention, the vibration isolation mechanism constructed in the foregoing manner is inserted between the axle configuration and the axle hub so as to be interposed therebetween. When the axle configuration is the drive shaft, the inner cylinder is fixed on the axle configuration, and the outer cylinder is fixed in a fitting hole of the axle hub. When the axle configuration is the non-drive shaft, the inner cylinder is fixed on the axle configuration similarly to the case of the drive shaft. However, the outer cylinder is pressed into the inside of the bearing loaded inside the axle hub.
For the vibration isolation mechanism attached when the axle configuration is the non-drive shaft, preferably, stiff pieces are respectively inserted into places located in the front and rear sides of the vehicle driving direction of the damping material in the vibration isolation mechanism. For the stiff piece, for example, a metal plate, a ceramic plate, a resin plate and the like can be used. By the insertion of such stiff pieces, the amount of variable displacement in the back-and-forth direction orthogonal to the axle configuration is reduced for the vibration isolation mechanism. Thus, the driving stability can be improved.
In addition, for the foregoing vibration isolation mechanism, preferably, an amount bxe2x80x2 of variable displacement upon application of a load in a direction orthogonal to the axial direction of the fastener (up-and-down direction of the vehicle) is set to be larger than an amount xcex4axe2x80x2 of variable displacement upon application of the same load in the axial direction (left-and-right direction of the vehicle). Because of the large amount xcex4bxe2x80x2 of variable displacement in the direction orthogonal to the axial direction of the fastener, ride comfort and road noise are reduced. Because of the small amount xcex4axe2x80x2 of variable displacement in the axial direction of the fastener, good driving stability can be maintained without being lowered.
Means for obtaining the foregoing characteristic can be achieved by setting a thickness axe2x80x2 of the damping material held in the axial direction of the fastener to be smaller than a thickness bxe2x80x2 held in a direction orthogonal to the axial direction, for example in the damping material provided between the outer and inner cylinders. In addition, the damping material provided between the outer and inner cylinders can be achieved by setting a difference in an elastic modulus between a damping material Axe2x80x2 held in the axial direction of the fastener and a damping material Bxe2x80x2 held in the direction orthogonal to the axial direction, and by setting the elastic modulus of the damping material Axe2x80x2 to be larger than that of the damping material Bxe2x80x2.